Abstract
A spectroscopic study of Hα has been carried out to investigate the properties of expanding chromospheres of late G and K supergiants. Spectra of 23 stars brighter thanV = 6.0 have been obtained at dispersions of 4–10 å mm-1 using the coude and the coudé-echelle spectrographs at the 102-cm telescope of Kavalur Observatory. The Hα profiles are all asymmetric in the sense that the absorption core is shifted to the blue by amounts ranging between -4 and -24 km s-1.
Hα profiles were theoretically computed using radiative transfer in spherically symmetric expanding atmospheres covering a large range of integrated optical depths. These were compared with the characteristics of the observed line in the programme stars. The analysis shows that the Hα line is formed in a region with velocity increasing outward. The computed equivalent widths and line core displacements were matched with those observed to obtain hydrogen column densities and expansion velocities. From these, the rates of mass loss in these stars were determined to be in the range of 10610-7 M⊙ yr-1.
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Vasu Mallik, S. A study of the H-alpha line in late G and K supergiants. J Astrophys Astron 3, 39–61 (1982). https://doi.org/10.1007/BF02714562
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DOI: https://doi.org/10.1007/BF02714562